Strange noise in studio, EMI, RF????

J

jamiecer

New member


For the past 1-1/2 years I've been working with John Sayers on my home studio. (I can't say enough good about him. Great guy! If you are on the fence about using him, just do it.) Yesterday, I went to start on the first session in my new room. I plugged in a Fender deville and got this strange ticking sound. The first thing I did is change the guitar cables, then the guitar, then the amp, still the sound persisted. I then moved the amp into another room, different breaker - same ticking. Next I turned off all the power to my house except for the one breaker providing power to room with the amp - same ticking. I moved the amp back to the original room and turned off the whole house again. Same ticking. I then unplugged the amp and set up a 57 running into a Rupert Neve Designs 5032 then an Avalon M5. Same ticking. Next I tried putting a ferrite choke on a guitar cable and plugging into the fender DeVille, again same ticking. I've tried ground lifting both the amp and the mic press and still here the ticking. This is where it gets strange. I have a pair of Dynaudio BM6A's and a pair of JBL LSR6332's with the matching sub running off a Crown MA-2402. The mic pres and monitors are run (for the time being) off the same 20 amp breaker. When I fire them up there is no ticking. The MP3 above is a recording of the Fender DeVille with a telecaster hooked up. If anyone has some ideas as to what this noise may be or how to get rid of it I'm very interested in hearing them. Oh yeah, last week I recorded upstairs in my house and the noise wasn't on the recordings I made. I went upstairs and plugged in the fender yesterday to check and surprise, it was there.

Thanks for any help you can offer,

Jamie
 
I'm confused, do you get the interference with the mic pres or not? Just with the 57 hooked up (that is, with the amps off)? If the problem happens with a 57 into your mic pres, I just don't know what to tell you. That is some pretty bad EMI. Beyond the clicking, the 60Hz hum is rather problematic.

If this is just an issue with the guitars and amps, then I'd say it's an EMI problem that seems to be external to your house. Your options in that case are limited; certainly I would move to shielded humbuckers and a fully shielded control cavity, beyond that you have to look at rewiring guitars, DIs, and amps for balanced input/output. The other much more expensive solution is to shield the studio . . .

Have you had an electrician check your panel connections and your house grounding scheme?
 
I never tried just the mic pre. When the 57 is plugged into any of my pres the noise is there. I guess the next thing to try is a different mic and cable combo then just the pres.

The electric panel is grounded via a single cold water ground.

The most bizzare thing is that the noises weren't there on my recordings last week.

Thanks for your reply

Jamie
 
reads to me its the Fender DeVille?

every room you took it...clicking...every other guitar and cable..into the F-Deville...clicking?

different rooms, house powered down ...only commonality is the Fender DeVille.

your other gear doesn't click...

tried another guitar amp?
 
Actually I tried plugging in a Mesa Boogie combo amp and it made the same sound. The mic pre amps as well are clicking. The only commonality I can see is the power coming in from the utility.
 
When I first built my studio years ago, I had a similar problem. It turned out to be my "recording" light (a sign over the door that I'd turn on when tracking like an "On The Air" sign at radio/TV stations, etc). It had a "flasher" installed in it to make it blink off and on. The flasher was the problem. I removed it and the issue went away. I'd start looking for stuff like that.
 
jamiecer said:
Actually I tried plugging in a Mesa Boogie combo amp and it made the same sound. The mic pre amps as well are clicking. The only commonality I can see is the power coming in from the utility.
Click to expand...

Perhaps, but we don't know if that is the source of the problem. If it's EMI, it would also affect battery-powered equipment. And noisy power alone shouldn't trouble gear with properly filtered power supplies; it has to be radiated as EMI (via a motor, dimmer switch, Track Rat's flashing sign, etc.) to leak into isolated circuits. Or you have a dirty ground or something. Or there is a transformer outside that is leaking noise.

It's puzzling that a 57 into a mic preamp would have induced noise though. The CMRR of that setup should be 60dB or more. What happens if you terminate an XLR cable plugged into a mic preamp with a 150 ohm (or so) resistor?
 
If the trouble was a dirty ground wouldn't a ground lift take care of that? Or would that travel down the neutral as well?

No cell phones were on. Actually that was the first thing I checked :)
 
"It's puzzling that a 57 into a mic preamp would have induced noise though. The CMRR of that setup should be 60dB or more. What happens if you terminate an XLR cable plugged into a mic preamp with a 150 ohm (or so) resistor?"

How would I make this termination? There is a radio shack nearby so should I be able to get the parts easily.
 
If the noise has a regular periodicity to it, it's probably not a dirty ground. Is it just the amp that makes noise?
 
Hi Track Rat,

I've also picked up the noise when I have a microphone plugged into a mic pre. The gain on the pre is turned almost all the way up, but it is there.
 
jamiecer said:
If the trouble was a dirty ground wouldn't a ground lift take care of that? Or would that travel down the neutral as well?
Click to expand...

By that I mean "not low impedance ground", which is pretty much the same thing a ground lift does. I think ground lifts are a band-aid on a sucking chest wound . . .

Yes, neutral connects to the same ground point as the ground wire. There should be very little resistance between neutral and ground. I don't think that is where your problem lies, but it's simple to check, and it's probably worthwhile to review all the panel connections while you're at it. Rule out the simple stuff, and it's good to check your connections for other reasons.

To do the resistor test, stick the resistor leads in pins 2 and 3 of the XLR. While you're at RS, pick up a multimeter, it's a useful thing to have. For example, you can measure the neutral-ground resistance at each outlet (make sure you check which is hot first!) If an outlet or many outlets are wired improperly, you'll find that out quick.

The basic problem is that you have an unknown noise source, probably external to your house. It seems to be causing interference in what is normally a very quiet, noise-resistant device--a transformer-balanced microphone into a balanced input mic preamp (are you also feeding your converters via a balanced connection?) If you can't fix that problem, it's probably hopeless for a guitar which is notoriously noisy.
 
do you have an aluminium case in the house or studio if so take the side cover off and put it in the studio make sure the noise is there and put it infront of things in the room see if the noise goes away the side panel should act as a shield to airbourne interferance aluminium is the next best thing to copper,unless you have some copper sheet lying about :D
 
Have you got any computer network cables running anywere near audio?

Fluro tubes in the lighting?

Cheers

Alan.
 
Hi Alan

There is a florescent light in my storage area, but it was turned off. And there is an ethernet cable running through the ceiling of my hallway. When I killed the power to the entire house I believe that would have killed any data transmission.

I am on Daddy Daycare for the next few hours then I should be able to go downstairs and further troubleshoot. Do you think removing the Florescent tube from the fixture would change anything or just being turned off is enough?

Thanks for your input. This is very frustrating as I have no idea where this noise is coming from. All advise is greatly appreciated.

Jamie
 
some tests

I was able to test the resistance between the AC Neutral and Ground. Unfortunately, they were never constant. They varied between 000.2Ω and 376.0Ω. I have no idea what this means.

The wiring from the mic pre to wall plate between pins 2 and 3 had a resistance of 112.2Ω or 112.3Ω every time I tested.

I also tested the polarity of my wall outlets every one of them is wired the same regardless of the circuit they are on.

Someone just recommended I try the Hum-X hum eliminator. I think I'll go to Guitar Center and pick one up to see if it helps.
 
jamiecer said:
I was able to test the resistance between the AC Neutral and Ground. Unfortunately, they were never constant. They varied between 000.2Ω and 376.0Ω. I have no idea what this means.
Click to expand...

0.2 ohms is good. They won't be constant as they will vary according to length and gauge of the wire. Essentially, you are testing the resistance of the ground wire and neutral wire as a circuit (they meet at the panel). 376 sounds high to me, but at least it's not open! Which outlet was that?


The wiring from the mic pre to wall plate between pins 2 and 3 had a resistance of 112.2Ω or 112.3Ω every time I tested.
Click to expand...

I am not sure exactly what you are testing here? This is an XLR wall plate? The DC resistance of the mic input is not really a meaningful number.
 
mshilarious,

Thanks for taking so much time in trying to help.

The outlet I tested was on the breaker that my mic pre's are plugged into. I just tested an outlet on the breaker that the guitar amp was plugged into. The multi-meter rear from 150.0Ω down to 000.3Ω and seemed to hover around 001.5Ω

I just returned from a neighbor's house. He has the same sort of ticking going through his home intercom system. Where does that leave me?

I was thinking about calling the local utility company to see if they know anything about this.

Jamie
 
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